1. Field of the Invention
The present invention relates to a solid-state imaging device formed by integrating a plurality of photosensors on a substrate in which a channel stop section for preventing leakage of electric charges between the photosensors can be effectively formed and to a method for manufacturing the same.
2. Description of the Related Art
FIG. 6 is an explanatory view of an example of the arrangement of a CCD solid-state imaging device.
The solid-state imaging device includes a photosensor (imaging region) 410, a CCD vertical transfer section 420, a CCD horizontal transfer section 430, an output 440 and so on in a substrate 400.
The photosensor 410 has a plurality of the CCD vertical transfer sections 420 along the respective photosensor trains, in which signal charges stored by the photosensors 412 are output to the CCD vertical transfer sections 420 and sequentially transferred in the vertical direction by the driving of the CCD vertical transfer sections 420.
The CCD vertical transfer sections 420 have the CCD horizontal transfer section 430 at the end, in which the signal charges transferred from the CCD vertical transfer sections 420 are output to the CCD horizontal transfer sections 430 line by line and sequentially transferred in the horizontal direction by the driving of the CCD horizontal transfer sections 430.
The output 440 receives the signal charges transferred by the CCD horizontal transfer sections 430 by a floating diffusion (FD), senses the potential of the FD by an amp transistor, and converts it to an electric signal for output.
The solid-state imaging device has a channel stop section for preventing charge leakage between the pixels along the vertical transfer direction (along the column of the photosensors) and the photosensor and between the photosensors along the horizontal transfer direction (along the row of the photosensors) and the CCD vertical transfer section (for example, refer to Japanese Unexamined Patent Application Publication No. 4-280675).
FIG. 7 is a sectional view of an embodiment of the channel stop section provided between the photosensors along the vertical transfer direction, showing a section taken along line A-A of FIG. 6.
As shown in the drawing, a photodiode region constituting a photo receiving section 510 of each photosensor has a P+ type impurity region 510A formed in the outer layer of a substrate 400 and an N-type impurity region 510B formed under the P+ type impurity region 510A.
Channel stop sections 520, or P-type impurity regions, are provided in the vicinity of opposite sides of the photodiode region along the vertical transfer direction.
Although transfer electrodes 550 of the CCD vertical transfer sections 420 and so on are provided on the top of the substrate 400 through a gate insulating film (not shown), their detailed description will be omitted here because they are not directly related to the present invention.
FIG. 8 is a sectional view of an embodiment of the channel stop section provided between a photosensor along the horizontal transfer direction and the vertical transfer section, showing a section taken along line B-B of FIG. 6.
As shown in the drawing, the photodiode region of each photosensor includes the P+ type impurity region 510A and the N-type impurity region 510B, as that shown in FIG. 7.
The CCD vertical transfer section 420 is formed on the side of the photodiode region through a readout gate.
The CCD vertical transfer section 420 is formed of an upper N-type impurity region 420A and a lower P-type impurity region 420B.
A channel stop section 520 that is a P-type impurity region is provided between the CCD vertical transfer section 420 and the photodiode region of the adjacent photosensor train.
The above-described solid-state imaging device has a conspicuous tendency to reduce the space between the vertical and horizontal photosensors with the reduction of the photosensor size owing to increasing number of photosensors and advancement toward miniaturization.
Therefore, the structure of the related-art channel stop section that is formed only in the outer layer of the substrate has the problem of not effectively preventing a phenomenon in which electric charges that are photoelectrically converted in the photodiode region are mixed to the adjacent photosensors (hereinafter, referred to as a color mixing phenomenon).
In order to prevent the color mixing phenomenon, it is necessary to increase energy during implantation of impurity ions to the channel stop section to thereby form the channel stop section deep in the substrate (along the depth of the bulk). However, when ions are implanted with high energy, the P-type impurity near the surface declines in concentration and so a smear component in the surface of the substrate cannot be reduced, leading an adverse smear phenomenon.
The ion plantation with high energy has the problem of easily causing dispersion of the P-type impurity, narrowing a charge storage region of the light receiving section (photodiode region), which decreases sensitivity and saturation signals.